The purpose of this Mentored Career Development Award is to support the candidate's development as an independent researcher well-versed in multi-level, multi-method study of interpersonal and internalizing trajectories in anxious solitary youth (youth who display socially anxious, shy, solitary behavior among peers). The research premises are that (1) the adaptive significance and developmental course of childhood anxious solitude (individual vulnerability) is moderated by interpersonal adversity (esp. peer exclusion, victimization), (2) protection and risk for peer adversity in anxious solitary children is moderated by individual, dyadic, and contextual (e.g., school environment) factors, (3) peer adversity predicts change in trajectories of social cognition and emotion regulation, (4) the relation between peer adversity and internalizing problems is mediated by social cognitive and emotion regulation processes. The conceptual guides for this research and training plan are a developmental psychopathology perspective and interactional child-by-environment model of development. The training plan will expand the candidate's capability to conduct research on a multi-level child-by-environment model of risk for psychopathology by extending her conceptual expertise beyond children's behavioral characteristics, peer relations, and internalizing problems to include both more micro- (emotion regulation processes) and macro-level concepts (e.g., school environment, dyadic relationships). Methodological training will enable the candidate to take a multi-method approach to her research by developing new expertise with behavioral observation and physiological assessment. Training will be accomplished during an intensive period of longitudinal research with three sponsors: Dr. Calkins (emotion regulation, physiological methodology;primary sponsor), Dr. Pianta (school context), and Dr. Rubin (anxious solitude) (all three have expertise in observational methods). This research will be conducted with a moderately-sized sample of anxious solitary children and an equal number of matched controls selected from an initial 3rd grade screening. These children and their school environments will be the subject of multi- method assessment on a biannual basis throughout the award period. In addition to these research and training activities, the candidate's career development plan specifies writing a series of empirical papers, regular publication and conference-presentation of empirical work, participating in advanced developmental colloquia, organizing relevant conference symposia, and, in the later phases of the award, crafting an R01. Public health statement: This research examines child and environment characteristics that distinguish victimized from non-victimized socially anxious, solitary youth. Youths'school environment, peer treatment, peer relationships, and behavioral and emotional functioning will be followed from 3rd to 7th grade.